Communication in a mine is vital, not only to ensure the safety of the miners, but also to coordinate the work effort. Because of the nature of an underground mine, there is a need for a reliable and satisfactory communication system. It will be appreciated that the environment of an underground mine system places considerable demands on a communication system.
In the prior art, there are known mine communication systems which are based on radio transmission. While it is possible to provide a working communication system, a radio-based system has its limitations. Firstly, a radio system is one-way, and therefore, communication between a miner and the surface is limited and can be broken. In addition, the characteristics of a mine, e.g. type of ore body and tunnelling, can affect the propagation of radio frequencies, thereby limiting the number of available channels for communication and accessibility of the communication system to the miners.
Furthermore, the communication system at the surface of a mine typically comprises a telephone system. A telephone system provides two-way communication and also provides a gateway to any number of emergency/rescue agencies. In practical terms this means that there are two communication systems operating on a mine site and while integrating the two systems is desirable, it can be expensive.
Another consideration for a communication system for use in an underground mine is the potential effect of electromagnetic radio waves propagating through the shafts. Since blasting caps can be ignited by radio signals having certain frequencies and/or power levels, the power level and frequency of signals utilized in a mine communication system must be a consideration.
Therefore, it is desirable to provide a communication system for use in a mine which can be integrated with the existing telephone system of the mine. It also desirable to provide the communication system with a two-way communication capability for full telephone service. Lastly, the transmission characteristics, e.g. power level and frequency range, of the system should provide optimum performance without any dangerous consequences in the mining environment.